IN ORDER TO UNDERSTAND MORE ABOUT THE EARLY RESPONSES OF ALFALFA ROOT HAIRS TO NODULATION FACTORS, WE USED THE NON-INVASIVE ION-SPECIFIC VIBRATING MICROELECTRODE TO DETERMINE THE TIME COURSE OF CALCIUM AND PROTON CURRENTS AROUND MATURE AND GROWING ROOT HAIRS BEFORE AND AFTER NOD FACTOR STIMULATION. IN GROWING ROOT HAIRS, THE CALCIUM GRADIENT INDICATES A NET EFFLUX OF PROTONS FROM THE ROOT HAIR TIP. NO SIGNIFICANT GRADIENT WAS OBSERVED IN NON-GROWING ROOT HAIRS. ROOT HAIRS PERFUSED WITH NODRM-IV (S) HAD A CONSISTENT AND DRAMATIC RISE IN PROTON EFFLUX WITHIN 5-7 MINUTES. THE RESPONSE OF THE CA++ FLUX TO NOD FACTORS WAS MORE COMPLICATED WITH AN OSCILLATING PATTERN OF CA++ INFLUX AND EFFLUX RECORDED AT THE ROOT TIP. THE NETWORK OF ACTIN PRESENT IN NORMALLY GROWING ROOT HAIR SHOWS CHANGES IN THE PATTERN OF STAINING AFTER APPLICATION OF NOD FACTORS OVER A PERIOD OF 12 HOURS (STUDIED WITH THE USE OF FLUORESCENCE VIDEO MICROSCOPY.) AFTER NOD FACTOR EXPOSURE, THE DYNAMIC CHANGES OF THE ACTIN FILAMENT NETWORK OVER TIME WERE FOUND TO INVOLVE BREAKDOWN AND REARRANGEMENTS. THE EARLY IONIC CHANGES IN RESPONSE TO NODULATION FACTORS ARE TEMPORALLY RELATED TO THE EARLY MEMBRANE DEPOLARIZATION REPORTED BY EHRHARDT ET AL. (SCIENCE 256: 998-1000, 1992) AND THE OBSERVED CHANGES IN THE ACTIN CYTOSKELETON AS WELL AS OTHER PREVIOUSLY OBSERVED REARRANGEMENTS (ALLEN ET AL.PLANT PHYSIOL. 96: 42, 1991) OF THE CYTOPLASMIC STRUCTURE.